The present invention relates generally to a method of making a nonwoven fabric exhibiting enhanced physical properties, including improved drape and hand, and more particularly to a method of making a nonwoven fabric comprising hydroentangling a precursor web at least partially comprising splittable filaments or staple length fibers, whereby the precursor web is imaged and patterned on a three-dimensional image transfer device.
Nonwoven fabrics are used in a wide variety of applications where the engineered qualities of the fabric can be advantageously employed. These types of fabrics differ from traditional woven or knitted fabrics in that the fabrics are produced directly from a fibrous mat eliminating the traditional textile manufacturing processes of multi-step yarn preparation, and weaving or knitting. Entanglement of the fibers or filaments of the fabric acts to provide the fabric with a substantial level of integrity.
U.S. Pat. No. 3,485,706, to Evans, hereby incorporated by reference, discloses processes for effecting the hydroentanglement of nonwoven fabrics. More recently, hydroentanglement techniques have been developed which impart images or patterns to the entangled fabric by effecting hydroentanglement on three-dimensional image transfer devices. Such three-dimensional image transfer devices are disclosed in U.S. Pat. Nos. 5,098,764, and 5,244,711, hereby incorporated by reference, with the use of such image transfer devices being desirable for providing fabrics with the desired physical properties as well as an aesthetically pleasing appearance.
For specific applications, a nonwoven fabric must exhibit a combination of specific physical characteristics. For example, for some applications it is desirable that nonwoven fabrics exhibit both wet and dry strength characteristics comparable to those of traditional woven or knitted fabrics. While nonwoven fabrics exhibiting sufficient strength can typically be manufactured by selection of appropriate fiber or filament composition, fabric basis weight, and specific process parameters, the resultant fabrics may not exhibit the desired degree of drapeability and hand as traditional woven or knitted fabrics exhibiting comparable strength. While it is known in the prior art to treat nonwoven fabrics with binder compositions for enhancing their strength and durability, such treatment can undesirably detract from the drape and hand of the fabric.
While manufacture of nonwoven fabrics from homopolymer, single component filaments or fibers is well-known, use of multi-component xe2x80x9csplittablexe2x80x9d fibers or filaments can be advantageous for some applications. These types of splittable fibers or filaments comprise plural sub-components, typically comprising two or more different polymeric materials, with the sub-components arranged in side-by-side relationship along the length of the filaments or fibers. Various specific cross-sectional configurations are known, such as segmented-pie sub-components, islands-in-the-sea sub-components, flower-like sub-components, side-by-side sub-component arrays, as well as a variety of additional specific configurations.
The sub-components of splittable fibers or filaments can be separated by various chemical or mechanical processing techniques. For example, portions of the multi-component fiber or filament can be separated by heating, needlepunching, or water jet treatment. Suitable chemical treatment of some types of multi-component fibers or filaments acts to dissolve portions thereof, thus at least partially separating the sub-components of the fibers or filaments.
U.S. Pat. No. 4,476,186, to Kato et al., hereby incorporated by reference, discloses various forms of multi-component fibers and filaments, and contemplates formation of structures wherein splitting of the fibers or filaments on one or more surfaces of these structures provides desired physical properties. This patent particularly contemplates treatment of the fibrous structures with polyurethane compositions, to thereby form synthetic leather-like materials.
The present invention contemplates formation of nonwoven fabrics exhibiting desired physical properties, including wet and dry strength characteristics, as well as good drapeability and hand.
The present invention is directed to a method of making a nonwoven fabric which includes imaging and patterning of a precursor web by hydroentanglement on a three-dimensional image transfer device. Notably, the precursor web at least partially comprises splittable filaments or staple length fibers, each of which comprises plural sub-components which are at least partially separable from each other. Attendant to hydroentanglement, the high pressure liquid streams impinging upon the precursor web act to at least partially separate the sub-components of the splittable filaments or fibers from each other, thus creating filament or fiber components having relatively small deniers. Because of the relatively reduced bending modules exhibited by the fine-denier sub-components, imaging and entanglement of the web is enhanced for fabric formation. The resultant fabric exhibits relatively high wet and dry tensile strengths, without resort to application of binder compositions or the like, and thus exhibits desirable drapeability and hand. By virtue of the fabric""s integrity, post-formation processes, such as jet dyeing, can be effected without the application of a binder composition, as is typically required.
In accordance with the disclosed embodiment, the present method comprises providing a precursor web at least partially comprising splittable, staple length fibers, wherein each of the splittable fibers comprises plural sub-components at least partially separable from each other. In presently preferred embodiments, splittable fibers having so-called segmented-pie and swirled configurations have been employed.
The present method further comprises providing a three-dimensional image transfer device having a foraminous forming surface. This type of image transfer device includes a distinct surface pattern or image which is imparted to the precursor web during fabric formation by hydroentanglement.
The precursor web is positioned on the image transfer device, with hydroentanglement effected by application of a plurality of high-pressure liquid streams. The high-pressure liquid streams act to entangle and integrate the fibers of the precursor web. By virtue of their high energy, the liquid streams at least partially separate the sub-components of the splittable fibers, thus enhancing the clarity of the image imparted to the precursor web from the image transfer device.
Depending upon the specific application for the resultant nonwoven fabric, various types of splittable, staple length fibers can be employed. In current embodiments, splittable staple length fibers have been used comprising nylon, and one of 1,4 cyclohexamethyl terephthalate and polyethylene terephthalate sub-components. It is also contemplated that the splittable fibers may be blended with staple length fibers selected from the group consisting of nylon, polyester and rayon.
Cross-lapping of a carded precursor web prior to positioning on the image transfer device desirably enhances the effect of the hydroentanglement treatment in patterning and imaging the precursor web. By virtue of the high degree of integrity imparted to the web attendant to hydroentanglement, the present method further contemplates that the nonwoven fabric can be jet dyed, subsequent to hydroentanglement, preferably without the application of a binder composition thereto.
A nonwoven fabric embodying the principles of the present invention can be formed to exhibit low air permeability, with the fabric thus being suitable for applications where the barrier properties of a fabric are important, such as for medical gowns and the like. The fabric is formed from a fibrous matrix at least partially comprising splittable, spunbond filaments, wherein each of the splittable filaments comprises plural sub-components at least partially separated from each other. Notably, the fabric has been found to exhibit desirably high strength and elongation, exhibiting permeability lower than a comparable melt blown fabric, while being three to four times stronger, with three to five times more elongation. Aside from medical applications, potential uses include filter media and personal hygiene articles.
Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims.